The Section works on (1) Understanding the interaction between antibodies and antigens; (2) The preparation of antibodies with specificity for the determinants occurring on glycoproteins, and the characterization of the interaction of these determinants with their antibodies; (3) The section retains an interest in the structural of fungal capsules. Concerning (1) the Section is working on two aspects of elucidating the details of antigen/antibody interaction. Firstly, we have developed a system to study the influence of hydrogen bonding in ligand-antibody binding. To this effect we have prepared a large number of galactose oligosaccharides in which certain hydroxyl groups have been selectively replaced by fluoro groups. If hydrogen bonding comes about by ligand-hydrogen donation these saccharides would bind less if the particular (replaced) position had been involved. If protein-hydrogen donation were the driving force, affinity would increase or remain similar. In this way we have been able to delineate the nature of the binding between a monoclonal antibody and its polymeric antigen in detail hitherto impossible to achieve. Secondly, we are trying to affinity-label the antibodies involved and this involves the synthesis of some complex reactive ligands. We are preparing oligosaccharidic (Bcta1, 6-linked galactosyl) derivatives with isothiocyanate or epoxypropyl as the reactive labelling group in order to label the monoclonal anti-galactan antibodies. Concerning (2) we have prepared eight synthetic immunogens bearing immunodeterminants known to occur on glycoproteins, and have obtained antibodies against several of these. At the moment we are purifying the antibodies and are trying to characterize them by affinity studies. These antibodies will be useful in characterization of glycoproteins on cell surfaces. Concerning (3) work was done on the immunodeterminants groups of aspergillus fumigatus, a pathogen in man.